In many analytical systems, discovering the nature of an unknown substance requires the substance to first be collected. There are detector systems that analyze a fluid flow analyte stream, e.g., vapors or gases, particulates, and liquid bound analytes. Some detector systems are based, for example, on an optical analysis that determines analyte characteristics by subjecting a quantity of the analyte to a light beam and measuring the scattering or fluorescence effects. Spectroscopic detector systems, for example, are sometimes based upon the optical effects produced by analyte samples. There are both quantitative and qualitative analysis detector systems.
Before a sample may be analyzed by spectroscopic or many other types of analytical techniques, the sample must be collected and then delivered to a detector system. Many samples of interest are available outside of a controlled setting. One important use for analyte analysis is for safety testing environments that humans occupy. There is a heightened awareness in modern times of the potential for the intentional detonation of explosives or release of chemical or biological agents into environments occupied by humans. For example, environments might include open or enclosed spaces in work environments, public environments, military environments, etc. Many building environments with ducted HVAC (heating ventilation and air conditioning) have the potential for the intentional release of TICS or chemical and biological agents into closed or open spaces occupied by military or civilian personnel. Manufacturing operations also have the potential to permit the escape of hazardous chemicals or biological agents into a manufacturing environment or to an external environment surrounding a manufacturing plant.
In some situations, detection may be desirable in a matter of seconds, but in others, an extended period of time may be used for collection before performing an analysis. An example of the latter case involves workers that may be exposed over a time period to unacceptable levels of harmful agents. Another example of the latter case is when cargo containers are transported from country to country by sea, in which case it may be desirable to collect a sample over a period of several days prior to analysis.
In uncontrolled settings and controlled settings, analytical resolution and the sensitivity of detection are dependent upon the efficiency of analyte collection and the efficacy of delivery of collected analyte to a detection system. It is desirable, for example, to detect very low levels of toxic or hazardous materials in a particular environment. Gas chromatography and other analytical techniques can employ a variety of detector types, and have been demonstrated to be very sensitive analysis methods, among other benefits. Another analytical technique employs a chemresistor based device, which uses a detector whose resistivity changes when it is exposed to particular chemical vapors. Whatever the type of detector system, however, concentrating analyte in a stage prior to the detector system can improve detection limits for the analyte(s) of interest, and can also provide a more reliable quantitative or qualitative determination of an analyte.
Constructing a portable field instrument for collection, storage, concentration, and possibly on-site analysis also presents challenges. Compactness is an important factor to provide an instrument that is useful in the field, but one that competes with other design constraints in the case of a portable field instrument. Among other important factors are the sensitivity discussed above, the time scale required to collect and analyze a sample (preferably short), the amount of fluid flow that may be achieved (limited by tolerable pressure drops and pump capacity) while maintaining good analyte-sorbent material interaction, and the amenability of a device's collection hardware to be integrated with other parts of a field instrument. Low weight, durability, and low electrical power consumption are also desirable qualities for prolonged field use.
It can be difficult to collect a sufficient amount of analyte in particular environmental conditions, such as in ambient surroundings having higher temperatures. For example, if a gas stream is warmer, it may interfere with the efficacy of the analyte collection system. On the other hand, cooling the sorbent material may help to reduce analyte bleed during a collection period. However, providing cooling for a collection device while also allowing for portability, ease of manufacture and use, and relatively low power consumption provides several challenges.